1. Technical Field
The present invention relates to a method of manufacturing a liquid crystal device, to a liquid crystal device, and an electronic apparatus.
2. Related Art
In an electronic apparatus, such as a cellular phone or the like, an electro-optical device, such as a liquid crystal device or the like, is used as a color image display unit. The liquid crystal device has a pair of substrates with a liquid crystal layer interposed therebetween. In order to form the liquid crystal device, first, a sealant (sealing material) is coated in a peripheral portion of a surface of one substrate. At that time, a liquid crystal injection hole is formed at a part of the sealant. Next, spacers are sprayed inside the sealant, and then the other substrate is bonded to the one substrate via the sealant. Accordingly, a liquid crystal cell is formed in an region defined by the pair of substrates and the sealant. Next, the liquid crystal cell is subjected to a vacuum for de-aerating and is then brought back to an atmospheric pressure while the liquid crystal injection hole is dipped into a liquid crystal vessel. In doing so, the liquid crystal cell is filled with liquid crystal by means of a pressure difference between the inside and outside of the liquid crystal cell and surface tension. When liquid crystal is filled in such a manner, however, the liquid crystal injection process takes an extremely long time. In particular, when a large substrate whose diagonal is more than one meter is used, it takes more than one day to entirely fill the substrate with liquid crystal.
Therefore, a dropping assembly method has been suggested in which liquid crystal is dropped onto one substrate in which a frame-shaped sealant is provided with no liquid crystal injection hole, and the other substrate is then bonded to the one substrate. According to this method, first, a sealant formed of thermosetting resin or the like is coated in a peripheral portion of a surface of one substrate. Next, a predetermined amount of liquid crystal is dropped onto the one substrate by a liquid droplet ejection device. Finally, the other substrate is bonded to the sealant under a vacuum atmosphere, the vacuum atmosphere is released to an air pressure atmosphere, and then the sealant is subjected to ultraviolet irradiation or heat treatment, thereby forming the liquid crystal device. For this reason, unlike the related art liquid crystal injection method, the sealant is formed in a ring shape with no injection hole.
According to this method, after both substrates have been bonded, the vacuum atmosphere is released to atmospheric pressure. Accordingly, a predetermined cell gap to which a uniform pressure is applied from both substrates can be obtained. Further, the cell gap can be determined according to the amount of liquid crystal dropped. For example, if the dropping amount is excessively small, the cell gap is thin, and thus air bubbles tend to occur. Further, if the dropping amount is excessively large, the cell gap is thick, and unevenness of the cell gap tends to occur. Therefore, by setting the desired optimum dropping amount of liquid crystal, a uniform cell gap can be obtained. Further, according to this method, unlike the related art liquid crystal injection method, the amount of liquid crystal used can be reduced, and the injection/sealing process can be omitted, such that tact time can be reduced.
In addition, as a method of forming the sealant, a method has been suggested in which a dispenser is used. See, for example, JP-A-2002-98979, JP-A-2003-222883, and JP-A-2003-241204, which are referred to as Patent Documents 1, 2, and 3, respectively. This method is a method in which, while relatively moving the dispenser and the substrate, the sealant is ejected onto the substrate in a predetermined pattern. Here, at a part of a peripheral portion of the sealant, the previously ejected sealant and the subsequently ejected sealant overlap each other, such that the sealant ejected on the substrate is formed in a ring shape. Accordingly, when the substrates are bonded after liquid crystal is dropped, the liquid crystal can be suppressed from leaking outside the ring-shaped pattern of the sealant.
The inventors have founded that, in the liquid crystal devices described in the above-described Patent Documents, it is difficult to stably form the sealant, a dummy space needs to be provided with respect to an adjacent panel, and the dispenser needs to be controlled at the beginning and end of drawing in order to form one pattern by one drawing operation. In addition, the inventors have founded that, in the method of forming the sealant by use of the dispenser, in general, a defective cell gap tends to occur.
As for an ejection method of a sealant by use of a dispenser, the inventors have found the following.
In such an ejection method, as shown in FIGS. 48A and 48B, the size of a drawing start portion 500 or a drawing end portion 510 needs to be formed to have the same size as those of other parts. This is because, when the size is excessively large, the cell gap is thickened, such that display unevenness occurs, and, when the cell gap is minute, liquid crystal may leak from that portion, such that reliability is degraded. When the sealant is drawn by a dispenser, in general, as shown in FIGS. 48A and 48B, at the drawing start portion 500 and the drawing end portion 510, the seal tends to be thickened or minuteness tends to occur. In addition, there are many cases in which, in order to make the size of a junction portion 520 uniform, the drawing start portion 500 and the drawing end portion 510 overlap each other, as shown in FIG. 48C. In this case, it has been confirmed that the length of the overlap portion is about 4 mm, and the width W2 of that portion is made larger than a predetermined target width W1 by about 0.1 to 0.2 mm (ΔW=W2−W1=0.1 to 0.2 mm) due to the variation in viscosity of the sealant or the like.
Further, in a TFD (Thin Film Diode) driving-type liquid crystal device or a liquid crystal device in which STN (Super Twisted Nematic) liquid crystal operates in a passive driving method, as shown in FIGS. 49 and 50, relay wiring lines 601 formed on a surface of a circuit board having driver ICs 600 and 610 and a common electrode (hereinafter, referred to as COM electrode) 602 formed on a counter substrate need to be electrically connected to each other via a conductive pad 603. In this case, conductive particles, in which the surface of a spacer is subjected to a plating treatment, are dispersed in the sealant, and the sealant is disposed on the conductive pad 603. As a result, the relay wiring lines 601 and the COM electrode 602 are electrically connected to each other via the conductive particles, and then an output potential of the driver IC 600 is applied to a wiring line of the counter substrate.
On the other hand, segment electrodes (hereinafter, referred to as SEG electrode) 604 relayed from the driver IC 610 up to a display area 620 or the relay wiring lines 601 relayed from the driver IC 600 up to the conductive pad 603 need to cross the sealant. In this case, as for the relay wiring lines 601 and the SEG electrodes 604, in order to prevent the individual electrodes from being electrically shorted, a sealant, which does not contain the conductive particles, is configured to cross the relay wiring lines 601 and the SEG electrodes 604.
By the way, as described above, when the sealant containing the conductive particles and the non-conductive sealant are used, from one end (A of FIG. 50) of the conductive pad 603 up to an end portion (B of FIG. 50) of the relay wiring line 601 crossing the sealant, both sealants need to be connected to each other. In the TFD liquid crystal device or the STN liquid crystal device, there are many cases in which the distance L between the end A of the conductive pad 603 and the end portion of the relay wiring line 601 crossing the sealant is set to be equal to or less than 2 mm. For this reason, if the distance L is simply made shorter than the length of the overlap portion shown in FIG. 48C, that is, 4 mm, it has been confirmed that, as shown in FIG. 48D, the length of the overlap portion of the junction portion 520 becomes 1 mm, the width W3 is made thicker than the predetermined target width W1 by about 0.5 to 0.6 mm (ΔW=W3 W1=0.5 to 0.6 mm), and thus a defective cell gap easily occurs.
Further, in Patent Document 1, the width of the overlap portion of beginning and termination for forming a seal line is set to be 0.4 to 0.6 times as small as the seal line width. In this method, however, the control of the dispenser is very complex, it takes a long time for drawing, the seal shape tends to be varied due to a variation in the amount of a residual sealant in the dispenser or a variation in viscosity between different lots of the sealant, and management is very difficult.
Further, in Patent Document 2, drawing starts from any portion outside the closed loop-shaped sealing member, and ends at a place outside the closed loop-shaped sealing member which is different from the portion where drawing starts. In this method, however, there is a problem in that a dummy space needs to be provided with respect to an adjacent panel. In addition, in any of the methods of Patent Documents 1 to 3, one member is formed by one drawing operation. Accordingly, there is a problem in that it takes time for the control of the dispenser at the beginning and end of drawing, and the tact extends.
Therefore, the inventors have accomplished the aspects of the invention on the basis of the above description.
An advantage of some aspects of the invention is that it provides a method of manufacturing a liquid crystal device which can realize a uniform cell gap, a liquid crystal device, and an electronic apparatus.